The present invention relates generally to nickel base alloys, and more particularly to Powder Metallurgy (P/M) nickel base alloys having improved characteristics.
Nickel base cast alloys have been extensively used for turbine parts and component designs requiring high temperature strength and corrosion resistance. Some of the more important characteristics needed for gas turbine components such as turbine rotor blades and disks include strength and ductility at elevated temperatures. In order to increase efficiency of gas turbine engine, it is desirable to operate such turbine rotor at the highest practical operating temperatures consistent with achieving the design lifetimes. The compositions of the present invention improve the performance of high work turbine engine designs, and thus provide the capability of operating such products at higher rim speeds. As a result, higher blade stresses and also higher stresses in the blade disk attachment and bore regions are able to be addressed and operating temperatures are able to exceed the capability of current disk alloys by about 200xc2x0 F. Various nickel alloy designs are known but fail to address the particular problems that are addressed within the context of the present invention. For example, U.S. Pat. Nos. 4,119,458, 4,668,312, 4,765,850, 4,3358,318 and 4,981,644 all disclose nickel base superalloy systems which are known. Similarly, U.S. Pat. Nos. 4,781,772, 4,719,080, 4,885,216, 5,330,711 and 5,370,497 also relate to nickel base alloys particularly suited for gas turbine engine compositions. As will be appreciated, alloys systems of the nickel base superalloy type are similar in many respects. However, differences in various components, particularly the refractory elements molybdenum, tungsten and rhenium can have significant impact on the strength of the alloy formed and improving the properties of the gamma matrix.
The present invention comprises a nickel base super alloy composition which can be fabricated into polycrystal articles having an exceptional combination of properties.
In general, it has been found that by controlling the ratio of molybdenum to tungsten or to the sum of tungsten and rhenium, alloy strength in terms of tensile, creep and rupture strengths for a given grain size and temperature range can be maximized. In the context of the present invention, the present inventors have found that these benefits are obtained by controlling the ratio of:             Mo      w        ⁢            or        ,      Mo          w      +      Re      
in the range of about 0.25 to about 0.5.
In general, the molybdenum is present in the nickel base superalloy compositions of the present invention in an amount between about 2 and about 3 weight percent whereas the sum of the tungsten and rhenium present in amount from about 4.5 to about 7.5. The broad composition range is thus from about 2 to 3 weight percent molybdenum, from about 4.5 to about 7.5 weight percent (tungsten plus rhenium.), from about 14 to about 18 weight percent cobalt, from about 10.0 to about 11.5 weight percent chromium, from about 3.45 to about 4.15 weight percent aluminum, from about 3.6 to about 4.2 weight percent titanium, from about 0.45 to about 1.5 weight percent tantalum, from about 1.4 to about 2.0 weight percent niobium, from about 0.03 to about 0.04 weight percent carbon, from about 0.01 to about 0.025 weight percent boron, from about 0.05 to about 0.15 weight percent zirconium with other elements optionally included in nickel base alloys.
In accordance with a further aspect of the present invention, the nickel base superalloys are substantially hafnium free and the sum of tantalum and niobium is in the range of about 2.5 weight percent.
Other features and advantages will be apparent from the specification and claims and from the accompanied drawings which illustrate an embodiment of the present invention.